1. Field of the Invention
The present invention relates to a multi-stage planetary gear train with at least forward 6 speeds that is adapted to an automatic transmission for motor vehicle.
2. Description of the Related Art
A multi-stage planetary gear train of this kind is disclosed in, for example, Japanese patent laying-open publication No. Tokkaihei 04-219553. This gear train has an upper-side planetary gear set providing a first fixed speed ratio and a lower-side planetary gear set of a double-pinion type, obtaining forward 6 speeds by 5 friction elements such as clutches and brakes.
The above known conventional multi-stage planetary gear train, however, encounter such a problem that concentric arrangement of the upper-side and lower-side sets requires the lower-side set to be double-pinion typed like gear trains shown in FIGS. 3 and 13 of the above publication. This restricts a construction of the lower-side set and its design freedom of speed ratios.
It is, therefore, an object of the present invention to provide a multi-stage planetary gear train which overcomes the foregoing drawbacks and can concentrically arrange an upper-side planetary gear set and a lower-side planetary gear set to enhance design freedom of speed ratios and obtain at least forward 6 speeds.